Letter regarding the article ‘Bending oxygen saturation index and risk of worsening heart failure events in chronic heart failure’
Authors: Tulika Ashok Kumar Nahar, Aishwarya Shah, Mahmood Ahmad
Journal: European Journal of Heart Failure (2022)

We read with interest the article by de la Espriella et al.1 which suggested that the use of a more objective clinical parameter named bending oxygen saturation index (BOSI) measuring oxygen saturation changes may be of more prognostic value in determining the risk of worsening heart failure (WHF) than bendopnea. We agree with the authors that bendopnea alone may not be associated with an increased risk of WHF events as indicated by the results (incidence rate ratio 1.04, 95% confidence interval 0.83–1.31; p = 0.705).1 This symptom being reported in a multitude of disease processes such as chronic obstructive pulmonary disease (COPD) by McDonnell et al.2 limits the precision and sensitivity of this prognostic tool. Patients who experienced shortness of breath due to non-cardiac reasons may have mistakenly been included, lowering reliability. It would be interesting to explore risk prediction in patients with multiple comorbidities. As shown by Karauzum et al.3 bendopnea is a useful indicator in assessing severity of pulmonary arterial hypertension which can culminate in right-sided heart failure. As nearly half of the patients in de la Espriella et al.'s had diastolic dysfunction, it might be useful to compare the effectiveness of both BOSI and bendopnea in patients with pulmonary arterial hypertension to see whether it can predict heart failure outcomes. Similarly, this can be done in patients with COPD (n = 17/112, 15.2%). A sub-population analysis of the predictive performance of BOSI and bendopnea for identifying recurrent WHF episodes in COPD participants could give more information about their widespread applicability. Furthermore, Kaya et al.4 investigated the relationship between bendopnea and clinical outcomes in stable heart failure patients finding positive results. The study included a questionnaire asking patients: ‘Do you experience shortness of breath while tying your shoelace?’ instead of an instantaneous assessment. Although subjective reporting of this symptom may be unreliable, it provided more information on the frequency and severity making it a less vague measure especially when breathlessness can be both lost and present in the same patient from time to time. There is ambiguity on how the symptom is reported in de la Espriella et al.'s study and a clearer statement in the methods section is warranted to elucidate how the presence/absence of breathlessness upon bending was registered, whether it was a physical finding or posed as a question. Nevertheless, a limitation remains where bendopnea is dependent on patient evaluation and is subject to different variations in symptom thresholds and understanding, all leading to a worse prognosis. The BOSI being a novel prognostic tool proposed by this study could be investigated further in studies. Whilst bendopnea alone may not be a good predictor, BOSI also has limitations and using both measures might provide more clinical utility in determining risk.